1. Field of the Invention
The present invention relates to a process and an apparatus for the powder coating of, for example, an automobile body (hereinafter referred to as work).
2. Description of the Related Art
FIG. 8 hereof is a flowchart showing a conventional process for coating an automobile body. The process includes Steps ST100 to ST102.
ST100 is the step of undercoating the work by eletrocoating. Its undercoating is done for making the work rustproof and enabling its top coating to form a surface maintaining a high level of luster.
ST101 is the step of intermediate coating the work by powder coating. Its intermediate coating is done for filling small flaws in its undercoating layer to obtain a smooth and lustrous finish and improving the durability of an overall coating on the work. Its powder coating is given by a paint having a color of, for example, high, medium or low brightness depending on the color of its top coating.
ST102 is the step of top coating the work. Its top coating is given for improving the appearance of the body and also protecting it. Its top coating is given by, for example, a paint having a light color such as beige, yellow or white, a paint having an intermediate color such as silver metallic, or a paint having a dark color such as black, dark blue, red or green.
If a paint having a light color is used for the top coating of the work, a powder paint having a color of high brightness is used for its intermediate coating. If a paint having an intermediate color is used for its top coating, a powder paint having a color of medium brightness is used for its intermediate coating. If a paint having a dark color is used for its top coating, a powder paint having a color of low brightness is used for its intermediate coating.
A powder coating apparatus is disclosed in, for example, Japanese Patent Laid-Open Publication No. SHO-62-71559. The apparatus includes spray guns, a recovery tank for recovering any powder paint sprayed by the guns, but not deposited on the work in a spray booth during one cycle of coating operation, a storage tank for storing the recovered paint, and a paint supply tank in which the recovered paint as supplied from its storage tank is mixed with a fresh paint supplied from its storage tank, so that their mixture may be supplied to the spray guns for coating the work during another cycle of coating operation. The apparatus can be used for coating a plurality of pieces of work continuously with a single kind of paint.
In the event, therefore, that three kinds of paints having high, medium or low levels, respectively, of color brightness have to be selectively used for intermediate coating as described above, it is necessary to employ a large scale of equipment including three lines of powder coating apparatus to be used with the three kinds of paints, respectively. If only a single line of apparatus is employed to make a compact scale of equipment, it is necessary to stop the operation of the line and remove the paint therefrom whenever a different paint has to be used for intermediate coating. This brings about a considerable reduction in the operating efficiency of the equipment. Moreover, the manual cleaning of the spray booth, or paint recovery tank is likely to allow the inclusion of dust or foreign matter in the paint.